We do not have a complete account for this species.

Although arguably the most studied nightjar in North America and one of the best known in the world, the Common Nighthawk remains poorly understood. Most studies of this species have been short-term and anecdotal in nature and specific data about much of its life history remain scarce, particularly from the southern part of its breeding range and especially from its South American wintering grounds.

This nighthawk is often observed on the wing, hawking insects at dusk and dawn in both urban and rural areas. Its loud, nasal peent calls, spectacular booming courtship dives, and erratic, almost bat like flight (hence the colloquial name "Bullbat") make this a reasonably familiar bird to anyone who spends time outdoors on warm summer evenings. In many ways, the name "nighthawk" is inappropriate for this bird because it is most active at dawn and dusk, not night, and like other members of its family, is not related to the hawks.

This is a species that actively pursues flying insects on the wing, often catching those attracted to streetlamps and other bright lights. Although it nests most often on open ground, gravel beaches, rocky outcrops, and burned-over woodlands, it was well known for its propensity to nest on flat gravel roofs, especially in cities. This habit is on the decline due to changes in roof construction practices. Whether nesting on roofs or natural sites, it makes no nest per se but usually lays its eggs directly on the ground; the cryptic plumage of this species makes nesting birds difficult to see. Both the female and male, which are similar in size and appearance, feed regurgitated insects to their chicks.

Recent (albeit limited) Breeding Bird Survey data suggest a substantial decline in numbers of this species, perhaps owing to increased predation, indiscriminate use of pesticides leading to lowered insect numbers, or habitat loss. It has been listed as Threatened in Canada -- a decline of about 50% has been noted there over the past 3 generations. In the United States it was listed in 2005 by Nature Serve as secure, but it is considered critically imperiled or imperiled in Connecticut, Rhode Island, New Hampshire, Vermont, and Delaware.

Nine subspecies have been recognized based on plumage color and size. Recent evidence suggests that the sub-family Chordeilinae (nighthawks) is polyphyletic, which would mean that the morphological specializations characterizing ¿¿nighthawks" evolved multiple times.